1. Field of the Invention
This invention relates to seals.
More particularly, the present invention relates to annular seals of the type especially adapted for use in connection with a mechanism having linearly or reciprocally movable members.
In a further and more specific aspect, the present invention concerns a seal apparatus having improved means for minimizing fluid leakage between the members and through the seal.
2. Prior Art
Various mechanical apparatus include first and second members which are substantially coaxial and disposed for relative reciprocal movement. Exemplary are internal combustion engines, positive displacement pumps, pneumatic motors and other mechanical devices incorporating a piston and cylinder assembly. Further examples will readily occur to those skilled in the art.
Commonly, the cylinder is defined by a bore having a cylindrical sidewall. The piston, a generally cylindrical member, includes a sidewall and a top. An end wall or head, opposing the top of the piston, closes one end of the bore. A chamber of variable capacity is defined within the bore between the head and the top of the piston.
Pressurized fluid functions within the chamber. In an internal combustion engine, the fluid is the expanding gases of combustion which serve to propel the piston downwardly or away from the head. Pressurized fluid from an external source is introduced into the chamber of a pneumatic motor to force movement of the piston. In a pump, which is companion to the engine and to the pneumatic motor, fluid is compressed and pressurized within the chamber.
In order to provide for relative movement between the members, it is necessary that the diameter of the piston be of lesser dimension than the diameter of the bore. Frequently, substantial clearance is required. For example, it is well known that a piston is more sensitive to thermal expansion than is a cylinder. Accordingly, where heat is a factor, such as in an internal combustion engine, additional space must be provided between the sidewall of the bore and the sidewall of the piston to accommodate thermal expansion of the piston. The space, commonly referred to as sidewall clearance, is generally in the range of fifteen ten-thousandths of an inch to five one-thousandths of an inch, or greater.
For reasons which are immediately apparent to those having an appreciation for the art, it is necessary that the piston be sealed to the cylinder. Conventionally, this is accomplished by a device commonly referred to as a piston ring, an annular seal usually fabricated of metal such as cast iron and having a generally rectangular cross-section. The ring is received within a mating annular ring groove formed into the sidewall of the piston. To facilitate expansion during installation, and for other reasons, the ring is radially severed.
The spacing between the opposed ends of the severed ring, known as the end gap, serves various functions after installation. Having an inherent tendency to expand, the ring maintains tension for attendant sealing against the sidewall of the cylinder as the bore increases in diameter as a result of wear. The end gap also allows for thermal expansion of the ring resulting from heat generated by friction, compression of fluid, combustion of fuel and other sources.
Although necessary and even beneficial, the end gap is also the source of considerable concernment. Normal end gap clearance in a newly installed ring ranges from approximately ten one-thousandths of an inch to approximately forty one-thousandths of an inch. The end gap defines a path for leakage of fluids between the sidewall of the piston and the sidewall of the bore. Throughout the life of the device, the piston ring continuously expands as compensation for normal wear. Resultingly, the end gap ever increases with corresponding increase in leakage, usually referred to as a blow-by.
Efficiency, economy and service life of the apparatus is directly related to blow-by. In general, less than optimum output of the apparatus results from loss of pressure or compression of the fluid. Other deleterious effects are unique to the particular apparatus. In an internal combustion engine, for example, contaminating by-products of combustion suspended in the blow-by gases are carried into the lubricating system which in turn harms components throughout the engine.
In recognition of the desirability of enhancing the seal between the piston and the cylinder, the prior art has proposed various seals which purportedly reduce or eliminate blow by. Several prior art proposals are direct at attempts to eliminate the end gap in the conventional piston ring. Various proposals include an insert which spans the end gap and is received in a notch formed into the ring on either side of the end gap. Other proposals include the use of a relatively thin steel member, alternately named a ribbon member or a gap seal member, having a substantially rectangular cross-section. Also advanced is a plurality of severed annular members, installed in stacked arrangement with staggered end gaps. The prior art has also advocated the use of thin steel members, colloquially dubbed rails, in combination with ring members having a general resemblance to conventional piston rings. Being of substantially heavier construction than a rail and usually fabricated of malleable material, such as cast iron, the ring member is variously referred to as a packing member or a sealing ring. The ring member in combination with the rail member comprise a seal assembly of which various embodiments are known.
In accordance with one known arrangement the rail resides within an annular groove formed into the inner circular wall of the seal member and exerts outwardly directed radial pressure to hold the seal member in contact with the sidewall of the bore. In another configuration, the rail occupies a space between the top of the seal member and the upper radial surface of the containing ring groove. Still other formations orient the radial axis of the rail at an angle.
For various reasons, annular seals of the foregoing character are not perceived as being entirely satisfactory. For example, in an assembly wherein the rail resides within the seal member and exerts an expansive force, excessive friction is generated against the sidewall of the bore. Where only the rail contacts the sidewall, seating or breaking-in of the seal is substantially retarded or even prohibited. An angled rail is subject to vibration, commonly known as ring flutter, when used in connection with a rapidly reciprocating piston. A thin steel member exposed to extreme heat, such as when utilized as the top compression ring in an internal combustion engine, will be become distorted.
Seal assemblies of the above character where devised mainly during the time period ranging from approximately the middle nineteen thirties to early nineteen fifties. During the early nineteen seventies, there was developed a seal assembly which substantially remedied the foregoing deficiencies inherent in the prior art. Distributed by POWERFORMANCE INTERNATIONAL CORPORATION under the trademark TOTAL SEAL.RTM., the seal assembly has achieved commercial success, especially for use in connection with four-cycle internal combustion engines.
Briefly, the Total Seal.RTM. device, referred to as a ring set, includes a sealing ring member and a gap seal member. The sealing ring member, a severed annular member preferably fabricated of malleable metal such as cast iron, has thickness and radial dimensions to be received within a conventional piston ring groove in accordance with standard tolerances. Extending inwardly from the outer cylindrical surface along the underside of the sealing ring member is an annular notch in which is received the gap seal member. The intricacies and advantages of the ring are described in U.S. Pat. No. 3,811,690 and are well known to those having regard for the art.
Notwithstanding continuing success in the trade, the Total Seal.RTM. ring set has proven to be less than optimum. As installed, the respective end gaps of the sealing ring member and of the gap seal member are diametrically opposed. The elastic expansiveness or outward radial force of a severed annular seal under tension is gradiently distributed throughout. Therefore, while the set as an assembly is free to move or work within the ring groove, theoretically, movement between the members should be prohibited as the result of the relative forces therebetween.
Extensive use in testing has shown that occasionally relative movement will occur between the members. The ultimate relative movement is capable of aligning the respective end gaps. While the other advantages of the set remain, leakage can occur.
Considerable research and development has been directed to devising a ring set which will retain the numerous benefits of the present Total Seal.RTM. ring set and yet provide additional benefits and resolve other problems of long-standing in the art. Substantial attention has been directed to an assembly in which the possibility of leakage is minimized. Additional efforts were directed to ameliorating the advantages of the ring set in such areas as reducing generated heat and increasing ring stability. Further consideration has been given to extending the utility of the assembly for use in additional applications, including internal combustion engines having sleeve or port valves and to making practical a piston having a single compression ring.
A foregoing investigation was particularly concerned with a seal assembly to be carried by a reciprocally movable member for sealing engagement with the bore within which the member is disposed. Once the problem solving efforts were set in motion, attention was directed to allied mechanical apparatus having members disposed for relative reciprocal movement. Especially considered was the converse yet correlative, subject of a seal assembly for sealing engagement with the movable member.
Exemplary, and chosen for purposes of extended research and development, is the valving apparatus of a conventional internal combustion engine. As will be appreciated by those skilled in the art, the assembly includes a valve having a shaft or stem which is movably disposed within a bore or valve guide carried by the head. The upper end of the shaft projects beyond the bore to reside within an oil ladened environment. The lower end of the shaft similarly projects beyond the end of the bore and communicates with the combustion chamber.
The typical internal combustion engine includes an intake valve assembly and an exhaust valve assembly. In response to normal engine operation, the assemblies are subject to forces which tend to cause the flow of fluids between the stem and the bore. During the intake cycle, during which the intake valve is open and a vacuum exists within the combustion chamber, a tendency exists for oil to be drawn through the assembly. During the exhaust cycle, during which the exhaust valve is open and the combustion chamber is pressurized, the tendency exists for exhaust gases to escape between the bore and the shaft.
It is apparent from the foregoing that sealing the valve assembly is an area of urgent concern. The prior art, however, has not provided satisfactory solution. Consistent with a teaching of the prior art, fluid flow is minimized by closely fitting the shaft within the bore. However, due to normal wear the clearance between the shaft and the bore ever increases resulting in progressively worsening blowby. As a purported solution, the prior art has provided valve seal devices which are secured to the upper end of the valve guide. While wear is of a lesser concern, such seal devices prevent adequate lubrication of the assembly.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide improved means for sealing between a pair of coaxial components having relative reciprocal movement therebetween.
Another object of the invention is the provision of improved sealing means especially adapted for use in connection with internal combustion engines, positive displacement pumps, linear fluid actuated motors and other apparatus having a bore encircling a piston, shaft or other reciprocally movable component.
And another object of this invention is to provide an improved annular seal of the normally severed type as exemplified by the conventional piston ring.
Still another object of the invention is the provision of a seal assembly having ameliorated means for materially reducing the possibility of leakage between the bore and the reciprocally movable member.
Yet another object of the immediate invention is to provide a seal assembly having rapid seating or break-in characteristics.
And yet another object of the invention is the provision of a seal device which will provide excellent sealing with substantially reducing friction.
And a further object of the instant invention is to provide a seal device having an extended service life.
Still a further object of this invention is the provision of a seal device which is easily installed with prior art skills and tools.
Yet a further object of the invention is to provide a seal device which is readily produced in accordance with known manufacturing techniques.
And still a further object of the invention is the provision of a seal device according to the foregoing which is adapted for use in mechanisms having an opening in the sidewall of the bore.
And yet a further object of the invention is to provide improved means and method for lubricating an assembly while maintaining a seal between the relatively movable components.